Biology in Human Welfare (LAQs)

Zoology-1 | 6. Biology In Human Welfare – LAQs:
Welcome to LAQs in Chapter 6: Biology In Human Welfare. This page includes the most important FAQs from previous exams. Each answer is explained in simple English, followed by a Telugu explanation, and then presented in the exam format. This approach will help you prepare effectively and aim for top marks in your final exams.

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LAQ-1 : Explain the structure and life cycle of entamoeba histolytica with the help of neat labelled diagrams.

Introduction

Entamoeba histolytica, a parasitic amoeba, is the causative agent of amoebiasis, primarily affecting the human intestinal tract. Understanding its structure and life cycle, including the stages of trophozoite and cyst, is crucial for comprehending its pathogenicity and transmission.

Structure of Entamoeba histolytica

1. Trophozoite Stage:
   • Appearance: The trophozoite is the active, feeding stage, appearing as a small, motile amoeba.
   • Size: Approximately 10-60 µm in size.
   • Features: It has a clear ectoplasm and a granular endoplasm, with a single nucleus that possesses a central karyosome and peripheral chromatin.
   • Function: This stage is responsible for tissue invasion and damage in the host.
2. Cyst Stage:
   • Appearance: The cyst is the non-motile, infectious stage.
   • Size: Typically about 10-20 µm in diameter.
   • Structure: It has a protective wall, making it resistant to environmental conditions.
   • Features: Mature cysts contain four nuclei, each with a karyosome and peripheral chromatin.

Life Cycle of Entamoeba histolytica

1. Ingestion of Cysts:
   • Transmission: Humans ingest cysts through contaminated food or water.
2. Excystation in Small Intestine:
   • Transformation: In the small intestine, cysts undergo excystation to release trophozoites.
3. Trophozoite Multiplication:
   • Colonization: Trophozoites multiply by binary fission in the large intestine and may cause ulcers and lesions.
4. Cyst Formation:
   • Encystation: Some trophozoites undergo encystation to form cysts in the large intestine.
5. Shedding of Cysts:
   • Excretion: Cysts are excreted in feces and can contaminate food or water sources, perpetuating the cycle.

Summary

Entamoeba histolytica has two main stages: the motile trophozoite and the non-motile cyst. The trophozoite is responsible for invasion and damage to the host tissues, while the cyst stage is crucial for environmental survival and transmission. The life cycle involves ingestion of cysts, excystation to trophozoites, multiplication and tissue invasion, encystation, and excretion of cysts. Understanding this life cycle is essential for controlling and preventing amoebiasis.

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LAQ-2 : Describe the life cycle of plasmodium vivax in man.

Introduction

Plasmodium vivax is a protozoan parasite responsible for causing malaria, primarily in humans. Its life cycle involves complex developmental stages within two hosts: the Anopheles mosquito and humans. Understanding this life cycle is crucial for comprehending the transmission and pathology of malaria.

Life Cycle of Plasmodium vivax in Humans

1. Infection Through Mosquito Bite:
   • Inoculation of Sporozoites: Humans are infected when bitten by an Anopheles mosquito carrying Plasmodium vivax sporozoites.
2. Liver Stage:
   • Sporozoites Enter Liver: The sporozoites travel to the liver and invade liver cells.
   • Formation of Schizonts: Inside the liver cells, sporozoites mature into schizonts.
   • Release of Merozoites: Schizonts rupture, releasing merozoites into the bloodstream.
3. Blood Stage:
   • Invasion of Red Blood Cells: Merozoites infect red blood cells (RBCs).
   • Trophozoite Development: Inside RBCs, merozoites mature into trophozoites, then into schizonts.
   • RBC Rupture and Release of Merozoites: Schizonts in RBCs rupture, releasing new merozoites, which infect more RBCs. This leads to the cyclical fever associated with malaria.
4. Formation of Gametocytes:
   • Sexual Reproduction Phase: Some merozoites develop into male and female gametocytes.
   • Transmission to Mosquito: When a mosquito bites an infected human, it ingests the gametocytes.
5. Further Development in Mosquito:
   • In the mosquito’s gut, gametocytes develop into male and female gametes, which fuse to form zygotes.
   • Zygotes become ookinetes, then develop into oocysts on the mosquito gut wall.
   • Oocysts release sporozoites, which migrate to the mosquito’s salivary glands, ready to infect a new human host.

Summary

The life cycle of Plasmodium vivax in humans begins with the inoculation of sporozoites through a mosquito bite. The parasite undergoes liver and blood stages in the human host, causing clinical symptoms of malaria. Some parasites develop into gametocytes, which are taken up by mosquitoes, perpetuating the cycle. Understanding this cycle is vital for malaria control and treatment strategies.

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LAQ-3 : Describe the life cycle of plasmodium vivax in mosquito.

Introduction

The life cycle of Plasmodium vivax, a parasite causing malaria, involves critical stages within the mosquito, specifically the female Anopheles species. This cycle is essential for the transmission of malaria from one human host to another.

Life Cycle of Plasmodium vivax in Mosquito

1. Ingestion of Gametocytes:
   • Feeding on Infected Human: The mosquito becomes infected with P. vivax when it feeds on a human who has gametocytes in their blood.
2. Development in the Mosquito Gut:
   • Gametocyte Maturation: Inside the mosquito’s gut, gametocytes mature into male and female gametes.
   • Fertilization: The gametes fuse to form a zygote, which then develops into a motile form called an ookinete.
3. Formation of Oocyst:
   • Penetration of Gut Wall: The ookinete penetrates the mosquito’s gut wall and forms an oocyst on the exterior surface of the gut.
4. Sporozoite Development:
   • Maturation of Oocyst: Inside the oocyst, the parasite undergoes multiple divisions to form numerous sporozoites.
   • Rupture of Oocyst: When the oocyst matures, it ruptures, releasing sporozoites into the mosquito’s body cavity.
5. Migration to Salivary Glands:
   • Movement to Salivary Glands: The sporozoites migrate to the mosquito’s salivary glands.
6. Transmission to Human Host:
   • Inoculation during Feeding: When the infected mosquito bites another human, the sporozoites are injected into the bloodstream, beginning the infection cycle in the new human host.

Summary

The life cycle of Plasmodium vivax in the mosquito begins with the ingestion of gametocytes from an infected human host. The parasite undergoes sexual reproduction in the mosquito’s gut, leading to the formation of oocysts and subsequent development of sporozoites. These sporozoites migrate to the mosquito’s salivary glands and are transmitted to a new human host during a mosquito bite. Understanding this cycle is crucial for developing strategies to interrupt malaria transmission.

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LAQ-4 : Describe the structure and life cycle of Ascaris lumbricoides with the help of a neat labelled diagram.

Introduction

Ascaris lumbricoides is a parasitic nematode roundworm that primarily infects the small intestine of humans. These worms are part of the Ascarididae family, Secernentea class, and Oxyurida order, and are also commonly found in pigs.

Structure of Ascaris lumbricoides

1. Size and Shape: Adult Ascaris worms are cylindrical and taper at both ends. Females can grow up to 35 cm long, while males are generally smaller.
2. Distinct Features: They have a three-lipped mouth, and their cuticle is smooth.
3. Reproductive System: Males have a curved posterior end with copulatory spicules, while females have a straight body and a reproductive system designed for high egg production.

Life Cycle of Ascaris lumbricoides

1. The Egg:
   • Production: Adult females lay approximately 20,000 eggs daily.
   • Excretion: Eggs are excreted in human feces. Unfertilized eggs are non-infective, but fertilized eggs become infective.
   • Environmental Conditions: Infectiveness depends on external factors like warmth, moisture, and soil conditions.
2. The Larvae:
   • Ingestion and Hatching: When ingested, fertilized eggs hatch in the intestine, releasing larvae.
   • Migration: Larvae penetrate the intestinal wall, travel to the lungs, and then ascend to the throat.
   • Swallowing: Larvae are swallowed and return to the small intestine.
3. The Adult:
   • Maturation: In the small intestine, larvae mature into adult worms.
   • Reproduction: Adult females begin egg production.
   • Life Cycle Duration: The cycle from ingestion of infective eggs to oviposition is around 2 to 3 months.
   • Lifespan: Adult worms can live for 1 to 2 years.

Summary

Ascaris lumbricoides exhibits a complex life cycle, beginning with the excretion of eggs in feces and progressing through larval migration to different body parts. After returning to the small intestine, the larvae mature into adult worms, and the cycle continues. The life cycle can span several months, with adult worms surviving up to 2 years in the human host.

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LAQ-5 : Describe the life cycle of wuchereria bancrofti with a neat diagram.

Introduction

Wuchereria bancrofti is a filarial nematode worm, the primary cause of lymphatic filariasis, commonly known as elephantiasis. Its life cycle involves two hosts: humans (definitive host) and mosquitoes (intermediate host). This complex cycle is essential for understanding the transmission and prevention of the disease.

Life Cycle of Wuchereria bancrofti

1. Infection of Humans:
   • Mosquito Bite: The life cycle begins when a mosquito infected with Wuchereria bancrofti larvae bites a human.
   • Larvae Entry: Larvae (L3 stage) enter the human skin at the bite site.
2. Migration and Maturation in Humans:
   • Migration to Lymphatic System: The larvae migrate to the lymphatic system and develop into adult worms over approximately one year.
   • Adult Worms: Adult worms reside in the lymphatic vessels, where they mate and produce microfilariae.
3. Circulation of Microfilariae:
   • Release into Bloodstream: Microfilariae are released into the bloodstream, primarily circulating during the night to coincide with the feeding habits of mosquitoes.
4. Ingestion by Mosquitoes:
   • Mosquito Feeding: When a mosquito bites an infected human, it ingests microfilariae.
5. Development in Mosquitoes:
   • Maturation in Mosquito: Inside the mosquito’s gut, microfilariae shed their sheaths, penetrate the gut wall, and migrate to the thoracic muscles.
   • Development to Infectious Stage: Here, they develop into the infective L3 stage larvae.
6. Transmission to New Host:
   • Transfer to Mosquito’s Proboscis: The L3 larvae move to the mosquito’s proboscis.
   • Infecting Another Human: When this mosquito bites another human, the larvae are deposited on the skin, and the cycle repeats.

Summary

The life cycle of Wuchereria bancrofti involves two hosts and several developmental stages. Humans are infected through mosquito bites, where larvae migrate to the lymphatic system, mature into adults, and produce microfilariae. These circulate in the bloodstream and are ingested by mosquitoes during feeding. Within mosquitoes, they develop into the infectious L3 stage and are transmitted to new human hosts during subsequent mosquito bites.